In various lecture meetings, scientific publication assemblies and others, charts, photographs and the like are projected as enlarged onto a screen by using a slide projector and an overhead projector as a means for aiding explanation.
For preparation of a slide from an original, it has heretofore been a common practice that a 35-mm camera 61 is fixedly mounted on a supporting column 62 of a two-piece stand 60 in a disposition facing downwardly, as is shown in FIG. 2, wherein an original 64 disposed on a table plate 65 of the two-piece stand with the surface carrying an image facing upwardly is illuminated with a light source 63 such as a projection lamp or stroboscopic flash lamp and the image is taken by operating a shutter of the camera 61. In that case, operator has to adjust the height of the camera 61 mounted on the supporting column 62 in dependence on the size of the original 64, adjust the focus and determine the shutter speed, aperture value in consideration of the type of the original, the type of the light source and brightness. This procedure requires skillfulness, and it has been difficult to obtain a slide which can be used satisfactorily unless the operator is accustomed to handle the camera.
On the other hand, a diapositive for projection by an overhead projector has heretofore been prepared by coping an original image onto a transparent sheet by using an electro-photographic copying machine. With this procedure, however, only the image in black and white can be obtained. In recent years, color image enjoys higher popularity in the CRT display for a computer or the like, not to speak of television and photograph. The projected image in black and white is poor in impression.
Recently, a variety of instant slide films have been proposed which allow color slides to be prepared immediately after photographing by simplifying the development process. A color instant film pack suited for the application mentioned above is commercially available which allows a color diapositive for the overhead projector to be prepared in a simplified manner. However, for using this film pack, an expensive camera destined for use only with this film pack is necessary. Besides, troublesome procedure is required as in the case of the aforementioned photographing procedure for the preparation of slide by copying the original.
In view of the shortcomings of the hitherto known method of preparing the 35-mm slide and the color diapositive for the overhead projector by copying the original as described above, the inventor of the present invention has devised an image forming apparatus which is simple in manipulation as in the case of the copying machine and in which the 35-mm slide film as well as the diapositive for the overhead projector using the instant film pack can be easily prepared from the original.
In this image forming apparatus, a contact glass plate for supporting thereon an original is provided on a top plate of the main body of the apparatus, wherein light reflected from the original illuminated by an original illuminating light source over the whole surface thereof is focused through a focusing optical system having two exchangeable optical paths onto a 35-mm roll film or a film in a film pack loaded in a 35-mm film loading section and an instant film pack holder, respectively, which are provided in a casing of the main body of the apparatus to thereby effectuate exposure to light.
The instant film pack holder can be removably placed to a predetermined set position on the main body of the image forming apparatus, wherein after setting the holder at the predetermined position, a portion of the film of the film pack loaded in the holder which portion is located at an aperture for exposure is exposed to an original image in the state where a light shield plate for preventing sensitization of the film is pulled out.
For the purpose of mounting a monitor provided with a focusing glass in place of the film pack holder for monitoring the image position or the like when unused film remains within the film pack or for other purposes, necessity often arises for removing the film pack holder from the predetermined set position by moving it along the guide rail. In that case, if the holder should be removed in the state in which the light shield plate has been pulled out, the unused film is sensitized wastefully.
In view of the state of the art described above, it is an object of the present invention to provide an image forming apparatus which is so arranged that erroneous operation of removing the film pack holder in the state in which the light shield plate has been pulled out can be prevented without fail.